Effects of a New Synthetic Ionic Liquid on Caking Properties of Coals with Three Different Ranks

To reveal the molecular structure characteristics of the caking components in coal, three coals with different ranks were treated using a new synthetic ionic liquid (i.e., [N4441][NO3]), the combination of which is based on the effect degree of different anions and cations of ionic liquids on the caking properties of the coals. Additionally, the raw and treated coals were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman. The results showed that the caking index (G) values of the coals decreased after [N4441][NO3] treatment, and the destruction degree decreased with increasing coal rank. The decrease in G is related to the removal of some species during [N4441][NO3] treatment. FTIR and Raman showed that aromatics with 3 or more rings but less than that in graphite and long-chain aliphatics were removed. XRD showed that [N4441][NO3] treatment decreased the graphitization degrees of the coals. Additionally, a mechanism of destroying the caking property of coal using [N4441][NO3] is proposed. [N4441][NO3] treatment could decrease the contents of aromatics with 3 or more rings but less than that in graphite and long-chain aliphatics. Consequently, the caking property of coal is destroyed.